Volumetric plastic strain increment

Deviatoric stress tensor Norm of deviatoric stress Lode s angle for stress Second invariant of deviatoric stress Third invariant of deviatoric stress Strain increment tensor Elastic strain increment tensor Plastic strain increment tensor Volumetric plastic strain increment tensor... 

The result of a simple tension experiment for a metal is schematically shown in Fig. 2.17 with axes of axial stress ai and axial sdain 1 or deviatoric stress s and deviatoric strain e. In metals the volumetric plastic strain can generally be ignored (sP = 0) therefore we can treat the behavior as a uniaxial response. On the other hand, the shearing behavior of geomaterials is inevitably accompanied by volume changes that are plastic, therefore we have to modify the original flow theory developed for metallic materials (Kachanov 2005 Lubliner 1990). Note that in small strain plasticity we assume that the plastic increment de can be decomposed into incremental elastic and plastic components ... 

Schofield and Wroth 1968). Here e = n/(l- ) is the void ratio, n is the porosity and dsv = — defi is Vs times the volumetric plastic strain (positive for compression) it is related to the void ratio e and plastic increment of the void ratio de by... 

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